19.09.2024

Second generation satellites emit 30 times more stray radio waves than before

More than half the operating satellites in orbit are SpaceX Starlinks, which can leave light trails in long exposure images.ALAN DYER/VWPICS VIA REDUX

Leaking radio emissions from SpaceX’s Starlink satellites are impeding observations by some ground-based radio telescopes and may eventually blind them, a new study using the Netherlands-based Low Frequency Array (LOFAR) radio telescope has found. The company’s second generation satellites, which it began launching last year, emit up to 30 times more radio waves than the first generation, the LOFAR team reports today in Astronomy & Astrophysics.

The radio leakage is at much lower frequencies than the bands used by Starlink satellites to deliver internet to customers and communicate with ground controllers, so the LOFAR team concluded it is unintentional. But it is 10 million times brighter than the dim astronomical sources LOFAR and similar scopes study. For radio astronomers, observing while a satellite is in its field of view is like trying to see the faintest star visible to the naked eye next to a full Moon, says lead study author Cees Bassa of the Netherlands Institute for Radio Astronomy, which operates LOFAR.

Soon the interference will be continuous. More than 6000 Starlinks are already in orbit—more than all other operational satellites—and SpaceX has plans for tens of thousands. When that happens, it may become impossible for a wide-viewing telescope such as LOFAR to find an area of sky without a Starlink in it. “That’s sort of the worst nightmare,” Bassa says. “It’s a bit depressing how much worse it's gotten so quickly.”

Researchers at the Square Kilometre Array (SKA), a planned radio observatory in South Africa and Australia, have worked closely with SpaceX engineers to reduce radio emissions from earlier Starlinks. “It’s extremely disappointing to see that in this latest generation the emission is there and it’s brighter,” says SKA Observatory Director Phil Diamond.

SpaceX is revolutionizing access to space with its relatively cheap reusable launchers. The Elon Musk–led company has also found a successful space-based internet business with Starlink, which now has more than 3 million global users. With companies such as OneWeb, BlueWalker, and Shanghai Spacecom Satellite Technology also trying to launch large satellite constellations, researchers estimate there could be 100,000 in orbit by the end of the decade.

Five years ago, optical astronomers realized the low-orbiting satellites can brightly reflect sunlight, marring observations. SpaceX has modified its satellites to reduce their glare, although they are not yet dimmed to a level recommended by the International Astronomical Union. Then in 2020, radio astronomers became similarly concernedfollowing a study by SKA researchers, which found that emissions in Starlink’s communication band were leaking into nearby bands reserved for astronomy. They, too, won concessions from SpaceX.

Now, LOFAR has found signals at much lower frequencies, which suggests something on the satellites is unintentionally behaving as an antenna. The emissions cover a broad range of frequencies that overlap with those LOFAR uses to peer back in time to the formation of the universe’s first galaxies and even farther to the cosmic “dark ages” before the first stars lit up.

The LOFAR researchers also identified more brightly glowing satellites than publicly published orbital data accounted for. The researchers suspect the extras could be military Starlink satellites being deployed for a U.S. Department of Defense project called Starshield. If they’re right, the satellites are not as secret as the Pentagon thinks—and the interference problem could be worse than the public satellite numbers suggest.

SKA researchers have informed SpaceX about the latest LOFAR results, and the company is carrying out its own tests. SKA and SpaceX engineers are meeting next week to compare results. “We’re happy to help,” Diamond says. “Hopefully it can be corrected.”

Aaron Boley, an astronomer at of the University of British Columbia, agrees. He wants national regulators to force satellite operators to behave more responsibly. “This is a really big threat to radio astronomy.”

Quelle: AAAS